Seven women working in a factory where nanoparticles were used in paint fell ill with serious lung disease and two died, researchers in China reported.
Experts said the findings are the first clear evidence that nanoparticles can be hazardous to health and should be taken very seriously.
Nanoparticles, which measure one billionth of a metre, are found in tennis racquets, special non-sweat socks, medicines, sunscreen and paints.
Researchers writing in the European Respiratory Journal said nanoparticles were found deep in the lungs of the women who fell ill.
The study, by a team led by Yuguo Song, of the Occupational Disease and Clinical Toxicology Department at Chaoyang Hospital in Beijing, said all of the women were admitted to hospital for respiratory problems over the course of a few months, accompanied by itchy eruptions of the skin on the face and arms.
They were found to have a build-up of liquid around their heard and lungs which could not be treated.
A chemical in the paint, the patients' lung tissue and the liquid surrounding the lungs were all found to contain nanoparticles.
According to Yuguo Song, these particles must originate in the polyacrylate-based paints used by the women at work.
Researchers at Beijing Chaoyang Hospital, together with the Chinese Centre for Disease Control, carried out an investigation
"The workers, of peasant origin, were also completely unaware of workplace health and safety regulations and of the potential toxicity of the materials they were handling", explains Yuguo Song. "Their only protection, used sporadically, was cotton gauze masks."
He added: "It is clear that the symptoms, the examination results and the progress of the disease in our patients differ markedly from respiratory pathologies induced by paint inhalation."
He said the lung condition continued to develop even after the women were no longer exposed to the paint and no other people fell ill after the machinery at the factory was shut down.
Although the authors cannot be certain the nanoparticles caused the illness but said: "We call on scientists throughout the world to work together and address this new challenge."
Dr Andrew Maynard, Chief Science Advisor, Project on Emerging Nanotechnologies at the Woodrow Wilson International Center for Scholars, in Washington DC, said the researchers have not identified what the nanoparticles involved are made from or how much the patients had inhaled.
Nonetheless, he said: "This is the first clear case where there is an association between someone breathing in nanoparticles in the workplace and getting seriously ill. People should take this very seriously. The international research community should be galvanised by this."
He said there should be renewed efforts to examine workplace exposure to nanoparticles and ensure it is kept to a minimum.
